The present disclosure relates to a sheet stacking device in which a plurality of sheets can be stacked, and to a sheet conveying device and an image forming apparatus that include the sheet stacking device, and in particular, to a sheet stacking device having a function to determine whether or not a sheet stacking portion is in an abnormal state, wherein the sheet stacking portion is supported to be movable in the up-down direction, and to a sheet conveying device and an image forming apparatus including the sheet stacking device.
An image forming apparatus such as a copier includes a sheet stacking portion on which a plurality of print sheets are stacked. The sheet stacking portion is configured to receive a driving force from an electric motor such as a motor and be moved in the up-down direction. In this type of image forming apparatus, when the upper surface of the print sheets is lowered in position due to decrease of the print sheets on the sheet stacking portion, the sheet stacking portion is moved upward until the upper surface is recovered to the position before it was lowered. With this configuration, the upper surface of the print sheets on the sheet stacking portion is always set to a position at which a print sheet can be fed.
As a device that includes the sheet stacking device, there is known a sheet feed device that can detect whether or not an abnormal operation has occurred in the sheet stacking portion, based on the driving current of the electric motor. In this sheet feed device, an overload current value for detecting abnormality in correspondence with the print sheet size is set for each of driving controls for raising and lowering a sheet feed tray (i.e., the sheet stacking portion). When a measured value of the driving current of the electric motor is larger than the overload current value, the sheet feed device detects that the sheet stacking device is in an abnormal operation.